Question

Which one of the following monounsaturated fatty acids is not an omega-9 (\(\omega\)-9) fatty acid?

• A. Palmitoleic acid (C16:1, \(\Delta^9\))
• B. Erucic acid (C22:1, \(\Delta^{13}\))
• C. Elaidic acid (C18:1, \(\Delta^9\))
• D. Nervonic acid (C24:1, \(\Delta^{15}\))

Hint:

The omega classification (\(\omega\)-n) of any monounsaturated fatty acid can be computed directly using the formula: \(n = \text{Total carbons} - \Delta \text{ double bond position}\).

Answer 1

The Correct Option is A

Step 1: Understanding the Concept:
The omega (\(\omega\)) nomenclature system is designed to classify fatty acids based on the distance of their double bonds from the terminal methyl group of the carbon chain.
In this system, the terminal methyl carbon is designated as carbon-1 (known as the \(\omega\) carbon), and counting proceeds toward the carboxylic acid group.

Step 2: Detailed Explanation:
To identify the omega series for any given monounsaturated fatty acid, we subtract the carboxyl-end position of the double bond (represented by \(\Delta\)) from the total number of carbon atoms in the chain.
Let us compute this value for each of the provided options to determine their classifications:
For Palmitoleic acid (C16:1, \(\Delta^9\)), the total carbon count is 16 and the double bond starts at carbon 9.
This is calculated as: \[ 16 - 9 = 7 \] This indicates that Palmitoleic acid belongs to the \(\omega\)-7 series of fatty acids.
For Erucic acid (C22:1, \(\Delta^{13}\)), the total carbon count is 22 and the double bond is located at carbon 13.
This is calculated as: \[ 22 - 13 = 9 \] This indicates that Erucic acid is classified as an \(\omega\)-9 fatty acid.
For Elaidic acid (C18:1, \(\Delta^9\)), the total carbon count is 18 and the double bond begins at carbon 9.
This is calculated as: \[ 18 - 9 = 9 \] This indicates that Elaidic acid is classified as an \(\omega\)-9 fatty acid.
For Nervonic acid (C24:1, \(\Delta^{15}\)), the total carbon count is 24 and the double bond starts at carbon 15.
This is calculated as: \[ 24 - 15 = 9 \] This indicates that Nervonic acid is classified as an \(\omega\)-9 fatty acid.
Comparing these results, we can see that Palmitoleic acid is an \(\omega\)-7 fatty acid, while the remaining options are all \(\omega\)-9 fatty acids.

Step 3: Final Answer:
Therefore, Palmitoleic acid is the only monounsaturated fatty acid listed that is not an \(\omega\)-9 fatty acid, which corresponds to option (A).